An electromagnetic fuel injector driven by an electrical signal from an engine control unit is widely used in automotive internal combustion engines.
This type of fuel injector is classified as either a port-injection type or a direct-injection type. A fuel injector of the port-injection type is mounted on an intake piping and injects fuel indirectly into a combustion chamber, whereas that of the direct-injection type injects fuel directly into the combustion chamber.
In the fuel injector of the direct-injection type, the spray shape formed by the injected fuel determines the combustion performance. To obtain desired combustion performance, therefore, it is necessary to optimize the spray shape. The spray shape optimization is achieved by optimizing the spray direction and the spray penetration when the fuel is injected at a specified flow rate.
Japanese Unexamined Patent Application Publication No. 2008-101499 discloses a fuel injector that includes a valve element which is movable; a driver which drives the valve element; a valve seat which is adjacent to the valve element; and plural orifices which are positioned downstream of the valve seat. The plural orifices are formed in different angular directions with respect to the central axis line of a nozzle of the fuel injector.
It is known that the spray from a fuel injector is emitted substantially in axial direction in which a nozzle hole is machined. When the fuel injector has plural nozzle holes (orifices), as is the case with the fuel injector described in Japanese Unexamined Patent Application Publication No. 2008-101499, it is demanded that the accuracy of machining in the direction of a nozzle hole be enhanced. Further, the spray penetration correlates with the flow rate of the fuel injected from each nozzle hole. It is therefore demanded that flow rate be controlled for each nozzle hole. In addition, it is demanded that the direction and flow rate of each spray be individually controlled in order to optimize the state of an air-fuel mixture.
The fuel injector described in Japanese Unexamined Patent Application Publication No. 2008-101499 does not set the flow rates of plural nozzle holes individually. One of the methods to individually set the flow rates of plural nozzle holes is, for instance, to vary the diameter of the plural nozzle holes, respectively. More specifically, the flow rate of each nozzle hole can be individually set by increasing the diameter of a nozzle hole for higher flow rate and by decreasing the diameter of a nozzle hole for lower flow rate.
However, in order to vary the diameter of the plural nozzle holes, it is necessary to prepare tools that match the diameters of the individual nozzle holes. In other words, it is necessary to prepare plural machining tools that provide holes with a varied diameter appropriate for desired flow rates and use the different machining tool to machine each of the nozzle holes. The number of process to prepare the tools increases with an increase in the number of nozzle hole sizes. Consequently, the time required for machining setup and post-machining inspection gets longer than when the diameters of all the nozzle holes are same, causing an increase in manufacturing cost of the fuel injector.
Further, when using different tools for machining plural nozzle holes, it is necessary to change the employed tool or transfer a nozzle hole formation material to a different machining device. Therefore, the tool may be relatively displaced from the material, causing a decrease in accuracy of nozzle hole machining.
The present invention provides a fuel injector that has plural nozzle holes with the same cross-sectional shape and can individually set the flow rate of each nozzle hole.